The transformers package

Haskell 98 part of a monad transformer library, inspired by the paper
Functional Programming with Overloading and Higher-Order Polymorphism,
by Mark P Jones, in Advanced School of Functional Programming, 1995
(http://web.cecs.pdx.edu/~mpj/pubs/springschool.html).

This part contains the monad transformer class, the concrete monad
transformers, operations and liftings.